1. Field of the Invention
This invention relates to the field of optical processing, and more specifically to space integrating optical processors for performing real-time correlations, transforms, and other processing operations.
2. Description of the Prior Art
It is often desirable to process information-bearing signals of large bandwidth in real time. This is particularly true in communications and radar signals processing. General purpose digital computers are capable of performing many of these operations; however, because of their limited speed, they are incapable of performing any but the simplest of such processing operations in real time. Special purpose digital signal processors, configured as array processors, typically can perform real-time processing operations if the bandwidth of the signal and the data rate are not too large, and if a considerable expense is acceptable.
Because of their large time-bandwidth products and relative simplicity, optical processors represent an attractive alternative to processing high data-rate signals, and space integrating optical processors may be found in the prior art. Space integrating architectures are characterized by having one or more integrations essential to the result being performed by lenses.
Two-dimensional optical processors known in the prior art commonly utilize photographic film as an information source, thereby precluding effective real-time operation. When a real-time capability is required, a coherent light valve might be used. However, these relatively bulky and expensive devices suffer from spatial and temporal nonuniformities. Additionally, a highly complex electronic driving mechanism would also be required.
Shortly after the development of two-dimensional acousto-optical devices, experiments proved their applicability to optical processing. An example of these experiments is found in Said, R. A. K., and Cooper, D. C.: "Crosspath Real-Time Optical Correlator and Ambiguity Function Processor," Proc. IEE, v. 120, No. 4, April 1973, pp 423-428. The authors describe an apparatus in which a two-dimensional Bragg cell is utilized to generate ambiguity diagrams. Significant problems are mentioned in the article, including the generation of unwanted diffracted light components which must be filtered, and operability of the apparatus only if applied signals have a relatively small bandwidth. Apparently, little further reported research has been performed using two-dimensional acousto-optical devices to the present time.
U.S. Pat. No. 4,225,938 to Turpin, incorporated herein by reference, describes a two-dimensional time integrating acousto-optical processor utilizing two one-dimensional Bragg cells. Much of the structure described therein has direct applicability to my invention.